Is it more or less than was expected? It’s almost impossible to say. Estimates of the amount of antibiotics given to food animals in the United States are ferociously contested and plagued by squishy definitions and category creep. In 2000, the Animal Health Institute, which represents veterinary drug manufacturers, put total use at 17.8 million pounds. In 2001, the Union of Concerned Scientists, which campaigns (among other issues) to dial back use of agricultural antibiotics, estimated that 24.6 million pounds per year are used only for “non-therapeutic purposes” — that is, to make animals grow to market weight faster and to prevent them catching diseases in the close quarters of confinement agriculture.

The reason why antibiotic use on farms is a concern, of course, is because such use stimulates the emergence of drug-resistant organisms that move off the farm in animals, in groundwater, in dust, on the wind and in the systems and on the clothes of those who work there, and makes new resistance factors available to be swapped among bacteria. (For much more about that, see thesethreeposts and this long archive at my former blog.)

The FDA’s estimate comes as the agency has been moving to curb agricultural antibiotic use after years of non-action. Today’s report, which is very short — basically a table and a bunch of footnotes — is the direct result of a 2008 amendment to the Animal Drug User Fee Act of 2003, which required manufacturers to report yearly on sales of agricultural antimicrobials. (Here’s an FDA Q&A on the report background.)

More important, though, today’s report dovetails with the FDA’s new effort to curb antibiotic use in agriculture, which Commissioner Dr. Margaret Hamburg said in October would involve “very serious scrutiny.” (Video here.) The main instrument of that effort is a “draft guidance” that the FDA opened for public comment over the summer, “The Judicious Use of Medically Important Antimicrobial Drugs in Food-Producing Animals” (pdf here). The point of that guidance is to ask agriculture to voluntarily withdraw from use the ag drugs that are functionally identical to drugs that are important in human medicine — because if bacteria become resistant to those drugs when they are used in animals, that newly derived resistance will also affect humans, making common diseases difficult or impossible to treat.

In addition to the volume figure, the real value of today’s brief report may be simply to make clear just what antibiotics are used in agriculture. Take a look at the report table at right, which lists the animal drugs used by amount sold within drug classes. (Note that the amounts are given in kilograms.) It lists:

Aminoglycosides: Human versions include streptomycin and amikacin.

Cephalosporins: Human versions include Keflex and Rocephin.

Lincosamides: Human versions include clindamycin.

Macrolides: Human versions include erythromycin.

Sulfas: Human versions include half of the very common drug combos Bactrim and Septra.

Penicillins and tetracyclines: Yup, just what they sound like.

“NIR”: That’s FDA shorthand for “not independently reported” because they have few manufacturers or make up a small portion of the market. Among them are fluoroquinolones. Human versions: Cipro and Levaquin.

There’s much more to be said about the issue of antibiotic use in agriculture, especially because the lone piece of legislation addressing it, the Preservation of Antibiotics for Medical Treatment Act, is currently in lame-duck limbo. This report is an important piece of data for the ongoing debate.

Update: I asked some experts in the field to comment on the release of this data. Dr. David Wallinga, director of the Food and Health program at the Institute for Agriculture and Trade Policy in Minneapolis (also William T. Grant Foundation Distinguished Fellow in Food Systems and Public Health at the University of Minnesota School of Public Health) replied:

Clearly, antibiotic use in animal agriculture is huge, and as the FDA and CDC and WHO all agree, much of it is unnecessary. Data collection is important. But, because resistant bugs quickly adapt, we can’t afford to wait for data to take action to reduce antibiotic use wherever possible. That includes routine uses of antibiotics for cattle developing liver abscesses because they’re force-fed grain rather than grass, as well as antibiotics used to make animals get fatter faster.

Update 2: A day after the release of this report, Rep. Louise Slaughter (D-NY), author of PAMTA and a public-health microbiologist, commented on the data — and also said she’ll be reintroducing the legislation again in the next Congress in January.

This report illustrates the overuse of antibiotics in food animal production and makes a strong case for some common-sense limits on antibiotic use. We are putting millions of pounds of antibiotics into the food supply unnecessarily every year. This cannot continue and it’s my hope that these new data from the FDA will encourage even more members of Congress to join me next year when I reintroduce this legislation. Moreover, the FDA must move fast to issue strong regulations on antibiotic usage in agriculture.

Update 3: Tom Philpott, senior food and agriculture writer at Grist — and a farmer, so he knows the territory — covered the FDA report and this post in a very kind and typically forthright post of his own.